Gas tank under serious pressure (solved)

[Deleted]

I really have no idea what caused this, I know i didnt overfill it, and it continued to leak like this for a solid 5 minutes after I took the gas cap off. Its important to note too that initially i went to loosen the gas cap to let some of the fumes out since it was dripping overnight apparently and it exploded and shot gasoline everywhere with a good amount of force (thus why i had a rag stopping it from going everywhere). I'm gonna be replacing all the lines, the vent relief valves and the charcoal canister in the hopes that this solves it tomorrow but any outside input might be helpful as this seems to have only become a problem overnight.

[Minuit]

Sounds like the gas tank vent lines are either pinched or blocked. They originate at the top of the tank.

[Deleted]

16 minutes ago, Minuit said:

Sounds like the gas tank vent lines are either pinched or blocked. They originate at the top of the tank.

yup gonna get under there tomorrow since ill be at work until 10 tonight, do you know why it could have all of a sudden become a problem of them being pinched?

[Eagle]

I know you think you didn't overfill it, but I think you overfilled it. Gasoline expands quite a bit as it heats up, and the MJ fuel system is sealed to prevent the escape of vapors into the atmosphere. The fact that gasoline exploded out of the filler when you removed the cap shows that you system isn't leaking.

 

Do you stop filling the first time the nozzle shuts off, or to you "top off" after the auto-stop? When you filled up, was it at night? I see you're in Chandler, AZ. I used to have relatives in Chandler and the Phoenix area, and I've worked on projects in Tucson. I have some idea how hot it can get there mid-day, and what a difference there can be from nighttime temperatures to mid-day temperatures.

[Deleted]

13 minutes ago, Eagle said:

I know you think you didn't overfill it, but I think you overfilled it. Gasoline expands quite a bit as it heats up, and the MJ fuel system is sealed to prevent the escape of vapors into the atmosphere. The fact that gasoline exploded out of the filler when you removed the cap shows that you system isn't leaking.

 

Do you stop filling the first time the nozzle shuts off, or to you "top off" after the auto-stop? When you filled up, was it at night? I see you're in Chandler, AZ. I used to have relatives in Chandler and the Phoenix area, and I've worked on projects in Tucson. I have some idea how hot it can get there mid-day, and what a difference there can be from nighttime temperatures to mid-day temperatures.

yes I'm beginning to think thats the case too. Currently its just idling to burn some of the gas, I filled it last night and I did what I always do and stop after the first click. eaglescout526 pointed out that the previous owner may have swapped it and put in an aftermarket tank which have no baffles and that may have resulted in overfilling (learn something new every day). Ive never run into this before though so weird that it would just now start being an issue. If the issue persists after burning a good amount of gas today ill look into the other stuff. I probably still will just to be safe. I'm hoping youre right though and its just overfilled. This is definitely a first for me haha. I'm mostly upset about the paint getting ruined

[johnj92131]

Have to ask.  What else has been done to the fuel system before you had this issue?   Has the tank been  pulled out?  Has the fuel pump been replaced?

[Jeep Driver]

14 minutes ago, johnj92131 said:

Have to ask.  What else has been done to the fuel system before you had this issue?   Has the tank been  pulled out?  Has the fuel pump been replaced?

Agreed with your curiosity. 

 

Something is going on there. 

[Deleted]

9 minutes ago, Jeep Driver said:

Agreed with your curiosity. 

 

Something is going on there. 

nothing in the time ive owned it (about 3 months). Like i said earlier eaglescout526 pointed out that the previous owner may have swapped it and put in an aftermarket tank which have no baffles and that may have resulted in overfilling

[Minuit]

It's very easy to pinch the rollover valve lines when reinstalling the tank. Combine that with a really hot day and an overfull tank... The pressure has to go somewhere. Normally that's the charcoal canister, but if you have a restriction in your evap system it can cause these symptoms.

 

It shouldn't be a sudden onset though. Plugged vent lines consistently cause high fuel tank pressure, not just all of a sudden. Have you ever heard vapors escaping when opening the cap before?

[Deleted]

28 minutes ago, Minuit said:

It's very easy to pinch the rollover valve lines when reinstalling the tank. Combine that with a really hot day and an overfull tank... The pressure has to go somewhere. Normally that's the charcoal canister, but if you have a restriction in your evap system it can cause these symptoms.

 

It shouldn't be a sudden onset though. Plugged vent lines consistently cause high fuel tank pressure, not just all of a sudden. Have you ever heard vapors escaping when opening the cap before?

it always gives a little bit of a hiss when i open it, but never anything that really struck me as a problem. I'm talking about as much hiss as youd get when opening a can of soda or something but really nothing as big as this

[DirtyComanche]

21 minutes ago, Pirate_Staz said:

it always gives a little bit of a hiss when i open it, but never anything that really struck me as a problem. I'm talking about as much hiss as youd get when opening a can of soda or something but really nothing as big as this

 

Seems excessive at that even.  Maybe.  Maybe my soda is louder than yours.  Maybe I don't notice it because it's cold here most of the time.

 

If you force gas up the vent lines and into the charcoal canister, it saturates the charcoal, and then won't vent until it dries out again.

[Deleted]

4 hours ago, DirtyComanche said:

 

Seems excessive at that even.  Maybe.  Maybe my soda is louder than yours.  Maybe I don't notice it because it's cold here most of the time.

 

If you force gas up the vent lines and into the charcoal canister, it saturates the charcoal, and then won't vent until it dries out again.

I plan on replacing all that stuff anyway just to be on the safe side

[Manche757]

That is a scary scenario.  Exploding gas fumes/spray. Hate to think what might happen in an accident. 

 

If I fill up (I never top off) I can smell gas fumes outside but not inside the cab.  If I don't put more than 15 gallons in the tank, I don't get the fumes.  I do not get hissing sound when taking the cap off.  No gas has ever leaked on the ground.  Any ideas?  8(MJ, 4.0, 5 speed  80K miles. I do not know if tank is original or not.

[AZJeff]

16 hours ago, Eagle said:

I know you think you didn't overfill it, but I think you overfilled it. Gasoline expands quite a bit as it heats up, and the MJ fuel system is sealed to prevent the escape of vapors into the atmosphere. The fact that gasoline exploded out of the filler when you removed the cap shows that you system isn't leaking.

 

Do you stop filling the first time the nozzle shuts off, or to you "top off" after the auto-stop? When you filled up, was it at night? I see you're in Chandler, AZ. I used to have relatives in Chandler and the Phoenix area, and I've worked on projects in Tucson. I have some idea how hot it can get there mid-day, and what a difference there can be from nighttime temperatures to mid-day temperatures.

I will affirm Eagle's thoughts.

 

Ground temperatures down 10 feet are going to be 60 degrees, even here in AZ.  If the gas station tank has not been refilled recently, that is the temperature of the fuel you put into your tank when you refueled.    Now let that gas sit in a  tank in 110 degree air, and where the pavement under the truck is probably 140 degrees.   That fuel is going to heat up a bunch, probably close to air temperature.   And it will expand--a LOT.

 

Fix your vent lines, and all should be normal again.

[Deleted]

4 hours ago, AZJeff said:

I will affirm Eagle's thoughts.

 

Ground temperatures down 10 feet are going to be 60 degrees, even here in AZ.  If the gas station tank has not been refilled recently, that is the temperature of the fuel you put into your tank when you refueled.    Now let that gas sit in a  tank in 110 degree air, and where the pavement under the truck is probably 140 degrees.   That fuel is going to heat up a bunch, probably close to air temperature.   And it will expand--a LOT.

 

Fix your vent lines, and all should be normal again.

I'm pretty confident thats exactly whats happened, I'm fixing it all today though

[Minuit]

Another data point - I know my vent lines are setup correctly on my 91 (after having pinched them during a tank install) and I almost never hear any hiss whatsoever when opening the gas cap. In fact, it's hissed at me exactly once since fixing the vent lines, and that was a REALLY hot day and I think I had just pulled it out of the shade so the fuel was actively warming up at the time. When I had the vent lines pinched, it shot the gas cap at me once and hit me right in the face. Big difference.

[eaglescout526]

I wish I took pictures of the old vent valves when I changed them to fix the over flowing before the gas pump stops problem, but they looked as you would expect for being thirty years old, roasted like a marshmallow. But I did give him a few things to check while on the back channel. Luckily the vent system isn't as complex as say a modern vehicle like a 5.7L Hemi.

[gogmorgo]

12 hours ago, Manche757 said:

 

If I fill up (I never top off) I can smell gas fumes outside but not inside the cab.  If I don't put more than 15 gallons in the tank, I don't get the fumes.  I do not get hissing sound when taking the cap off.  No gas has ever leaked on the ground.  Any ideas?  8(MJ, 4.0, 5 speed  80K miles. I do not know if tank is original or not.

 

Mine did this for a while. Crusty old tank was seeping slightly. Never enough to make a puddle but enough there was a constant wet patch on the side of the tank, and the smell was quite noticeable – parked it in my parents' attached garage overnight once, and it was a couple days before you didn't get a wiff of gas walking into the house... whoops. 

It could also potentially happen if your vent lines have been disconnected. 

[Manche757]

6 hours ago, gogmorgo said:

 

Mine did this for a while. Crusty old tank was seeping slightly. Never enough to make a puddle but enough there was a constant wet patch on the side of the tank, and the smell was quite noticeable – parked it in my parents' attached garage overnight once, and it was a couple days before you didn't get a wiff of gas walking into the house... whoops. 

It could also potentially happen if your vent lines have been disconnected. 

What, if anything, did you do about it?  Wet spot from deteriorated tank?

[gogmorgo]

On July 23, 2019 at 5:39 AM, Manche757 said:

What, if anything, did you do about it?  Wet spot from deteriorated tank?

Not much until I mowed down a deer and it made the damage worse. My insurance bought me a new tank... took the body shop for friggen ever to track down the tank though. If it were me I'd just have got it off rockauto.com. 

[Deleted]

for those curious my charcoal canister is definitely clogged as my vacuum line running to it pulls vacuum normally but when i hook it up to the canister theres no vacuum on the vent line port coming from the tank.Hopefully the clogged canister is the problem.

[Ωhm]

2 hours ago, Pirate_Staz said:

theres no vacuum on the vent line port coming from the tank.

 

Isn't the canister vented to atmosphere through the charcoal?

[Deleted]

1 minute ago, Ωhm said:

 

Isn't the canister vented to atmosphere through the charcoal?

my vent line was routed into the charcoal canister which was then routed out into the intake manifold through a vacuum line so maybe thats wrong but its how mine was set up when I started checking things out. Regardless the canister is clogged so currently the vent line running from the tank is just hanging out until i clean or replace the canister

[Ωhm]

8 minutes ago, Pirate_Staz said:

then routed out into the intake manifold through a vacuum line

 

Check out page 75. Show vacuum routing. Should be the same as yours.

http://www.eriejeeppeople.com/Jeep_tech/87_90_fuel_injection_renix/Jeep_Renix_Fuel_Injection_manual.pdf

[Deleted]

1 minute ago, Ωhm said:

 

Check out page 75. Show vacuum routing. Should be the same as yours.

http://www.eriejeeppeople.com/Jeep_tech/87_90_fuel_injection_renix/Jeep_Renix_Fuel_Injection_manual.pdf

my drivetrain is out of a 96 cherokee but its pretty much exactly like that with the exception that my lines also pass thru some emissions thing (for lack of a better term) before getting to the throttle body. Its also plugged into the throttle body directly not the airbox. maybe I'm bad at wording things but I hope that makes sense.